Ultrasonic tranducer

ABSTRACT

An ultrasonic piezoelectric transducer and a method for measuring and/or monitoring the thickness of a wear member, in-situ, and the amount of wear that has occurred thereto, is disclosed. The transducer includes a sleeve which is received in a blind bore provided in the wear member, a piezoelectric element positioned within the blind bore, and an aligning spacer means interposed between the end of the sleeve and the piezoelectric element. By the application of appropriate voltage pulses to the piezoelectric element, the wall thickness between the bottom of the blind bore and the inner surface of the wear member can be measured.

TECHNICAL FIELD

The present invention relates to a method for measuring and/ormonitoring the thickness of a wear member and the amount of wear thathas occurred thereto, and more particularly to an ultrasonicpiezoelectric transducer for measuring and/or monitoring such thicknessand wear.

BACKGROUND ART

Various approaches have been devised for detecting, monitoring andmeasuring the amount of wear which has occurred to a wear member. Forexample, in the area of rotating equipment, a number of electricaldevices are available to detect and monitor bearing wear. These devicesare based upon a number of detection techniques. Thus, wear detectionmight depend upon the completion of an electrical circuit through thebearing when there is excessive bearing wear, or it might depend uponthe generation of a voltage if the shaft rotates eccentrically, or itmight depend upon the detection of an abnormal temperature rise of thebearing. Each of these approaches has some inherent disadvantages withrespect to accuracy and does not measure actual bearing wear or bearingwall thickness, i.e., each approach is responsive to bearing wear butdoes not measure quantitatively the amount of wear that has occurred orthe wall thickness remaining.

Other approaches have been devised to measure the thickness of aworkpiece or wear member, and by measuring such thickness, the amount ofwear which has occurred can be calculated. These approaches havenumerous commercial and/or industrial applications, however, their usefor measuring the wear of a work surface in-situ is cost prohibitive. Inaddition, these approaches typically utilize devices fabricated frommaterials which limit their applications to an operating environmenthaving a temperature of normally less than 75° C., and cause theresulting readings to be dependent upon the temperature of the operatingenvironment. It has also been found that the materials utilized forthese devices cannot withstand severe operating environments whichfurther limits the applications in which they can be used. Thus, thesedevices and measurement techniques are not usable for measuring and/ormonitoring the thickness of work surfaces, such as a sleeve bearing, inan elevated temperature operating environment such as might exist inrotating equipment. This inability to measure and/or monitor bearingwear in-situ can result in costly machine downtime to inspect thecondition of the bearings. Alternatively, this inability can result inunnecessary damage to the rotating equipment due to bearing failurewhich was not promptly detected.

Because of the foregoing, it has become desirable to develop a devicewhich can be utilized to measure and/or monitor the thickness of and theamount of wear which has occurred to sleeve or thrust bearings, brakediscs or pads, clutch plates and sealing members, in-situ.

SUMMARY OF THE INVENTION

The present invention provides an ultrasonic piezoelectric transducerthat can be mounted within the wall of a wear member, such as a sleeveor thrust bearing, brake disc or pad, clutch plate or sealing device, sothat measurements of wall thickness can be made in-situ. The transducerincludes an outer sleeve which is threadedly received in a blind borewithin the wear member, a piezoelectric element which is positionedwithin the blind bore, and spacer means interposed between the end ofthe outer sleeve and the piezoelectric element. The spacer means and theend of the outer sleeve have complementary configurations permitting thespacer means to align itself within the end of the outer sleeve andapply a substantially uniform compressive force to the piezoelectricelement. The application of such a substantially uniform compressiveforce causes a firm, electro-acoustical contact to be formed between thepiezoelectric element and the bottom of the blind bore which insures ahighly accurate measurement of the wall thickness between the bottom ofthe blind bore and the inner surface of the wear member. For example, ithas been found experimentally that this transducer can measure the wallthickness (0.100 inch) of a bronze bearing at 300° F. with arepeatability in the sub-micron range utilizing state-of-the-artelectronics. The transducers can also be located in a pre-determinedarrangement around the periphery of the wear member so that wear can bemeasured and/or monitored around the periphery thereof.

In an alternate embodiment of the invention, a mounting ring is providedto position one or more transducers against the outer surface of thewear member. In this embodiment, the piezoelectric elements contact theouter surface of the wear member and the total thickness of the wearmember is measured.

In still another alternate embodiment of the invention, the blind boreswithin the wear member are replaced with through bores to reduceproduction costs. A transducer assembly is received within each of thethrough bores so that its end is flush with the inner surface of thewear member. In this embodiment, the end of the transducer assembly isactually a part of the wear surface and the thickness of the end of thetransducer assembly is being measured.

Regardless of the embodiment utilized, a separate transducer may beplaced in the same environment as the other transducers for use as arelevant time reference.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial cross-sectional view of an ultrasonic piezoelectrictransducer embodying the invention of this disclosure and installed in awear member.

FIG. 2 is a partial cross-sectional view of a plurality of ultrasonicpiezoelectric transducers embodying the invention of this disclosure andinstalled in and around the periphery of a wear member, such as a sleevebearing.

FIG. 3 is a partial cross-sectional view of a mounting ring forretaining one or more ultrasonic piezoelectric transducers against theouter surface of a wear member, such as a sleeve bearing.

FIG. 4 is a partial cross-sectional view of an alternate embodiment ofan ultrasonic piezoelectric transducer embodying the invention of thisdisclosure and installed in a wear member.

FIG. 5 is a cross-sectional view of an ultrasonic piezoelectrictransducer used as a relevant time reference.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings where the illustrations are for thepurpose of describing the preferred embodiment of the present inventionand are not intended to limit the invention hereto, FIG. 1 is across-sectional view of the transducer 10 installed in a wear member 12,such as a sleeve or thrust bearing, clutch plate, brake disc or pad,sealing member or the like, whose thickness is to be measured and/ormonitored. The transducer 10 is comprised of an outer sleeve 14, analigning and electrically insulating spacer 16 received within the endof the outer sleeve, and a piezoelectric element 18.

The outer sleeve 14 is fabricated from round tubing, such as brasstubing or the like, which has threads 20 formed adjacent one endthereof. Typically, the tubing material has the same or similar thermalexpansion properties as that of the wear member 12 to maintain a firmcontact therewith. This firm contact is provided by the threads 20 whichengage complementary threads provided in the wear member 12, ashereinafter described. The threads 20 also permit the adjustment of theouter sleeve 14 within the wear member 12 to optimize the operation ofthe transducer 10 as later discussed. It should be noted that otherapproaches are possible for the adjustable attachment of the outersleeve 14 to the wear member 12, such as a bracket arrangement (notshown) that is adjustable with respect to the wear member 12 and whichretains the sleeve 14. The end 22 of the outer sleeve 14 has anindentation provided therein forming a surface 24 connecting the end 22of the sleeve 14 with the inner circumferential wall 26 of the sleeve.This indentation may have a curved configuration, such as semisphericalor parabolic, or it may have a conical configuration which is preferredto permit alignment of the spacer 16 therein.

The aligning and electrically insulating spacer 16 is fabricated from aceramic or ceramic-like material that is capable of sustaining hightemperatures and high pressures. For example, pyrolytic boronitride oranother ceramic-like material can be used for the spacer 16. Theparticular ceramic or ceramic-like material utilized for the spacer 16is selected to compensate for the thermal expansion properties of theother components comprising the transducer 10 and the wear member 12 sothat the spacer 16 will maintain a substantially uniform compressiveforce on the piezoelectric element 18 over a broad operating temperaturerange. The spacer 16 typically has a conical configuration that iscomplementary to that of the indentation formed in the end 22 of theouter sleeve 14. The spacer 16 is received within the indentation sothat the outer surface 28 defining its conical configuration contactsthe surface 24 formed by the indentation. The use of conical surfaces24, 28 formed on the outer sleeve 14 and the spacer 16, respectivelypermits the alignment of the spacer 16 within the outer sleeve 14through elastic deformation of the spacer 16 and the indentation formedin the end 22 of the outer sleeve 14. In contrast, self-alignment of thespacer 16 within the outer sleeve 14 can be achieved by using asemi-spherical or parabolic configuration for the surfaces 24, 28 formedon the end 22 of the outer sleeve 14 and the spacer 16, respectively. Itshould be noted that regardless of the shape of the complementaryconfigurations used for the spacer 16 and the indentation in the end 22of the outer sleeve 14, a precise fit of the spacer 16 within theindentation is not necessary since any deviations in size or shape willbe compensated for by the elastic deformation of the spacer 16 and theindentation and/or by the self-alignment of the complementary curvedsurfaces. The alignment of the spacer 16 within the outer sleeve 14,whether by elastic deformation of the spacer 16 and the indentation inthe end 22 of the outer sleeve 14 or by self-alignment throughcomplementary curved surfaces, is necessary to ensure the application ofa uniform compressive force on the piezoelectric element 18. Such asubstantially uniform compressive force also minimizes the possibilityof damaging the piezoelectric element 18 through the application of anonuniform compressive force thereto. Even though both of the foregoingapproaches apply a substantially uniform compressive force to thepiezoelectric element 18, it has been found that the use of anappropriate conical configuration for the spacer 16 and the indentationin the end 22 of the outer sleeve 14 is easier to implement and mayresult in a substantially higher absorption and obliteration of spuriousechoes from the primary ultrasonic signal than if complementary curvedconfigurations are used for the spacer 16 and the indentation in the end22 of the outer sleeve 14. Thus, the use of a conical configuration forthe spacer 16 and the end 22 of the outer sleeve 14 results in a highersignal to noise ratio than if complementary curved configurations areused for same. In summary, the spacer 16 is necessary in this structurein order to provide a substantially uniform compressive force to thepiezoelectric element 18 and to absorb and obliterate spurious echoes.Regardless of the configuration utilized for the spacer 16, an aperture30 is formed therethrough. This aperture is sufficiently large to permitthe passage of an electric conductor therethrough.

The wear member 12 whose thickness is to be measured and/or monitored isprovided with a blind bore 36 therein. The blind bore 36 is located soas to be substantially perpendicular to the outer and inner surfaces 38,40, respectively of the member 12. If the member 12 is a sleeve bearing,the blind bore 36 is directed radially inwardly so as to beperpendicular to tangents which intersect its centerline on the outerand inner surfaces 38, 40 of the member 12. The blind bore 36 is of apredetermined depth and has a substantially flat surface 42 at thebottom thereof. The distance between the flat surface 42 and the innersurface 40 of the member 12 is the distance to be measured and/ormonitored. The blind bore 36 may also have threads 44 formed thereinwhich terminates adjacent the bottom thereof.

The piezoelectric element 18 is a standard state-of-the-art device andtypically has a round disc-like shape. The element 18 can be formed fromcommercially available piezoelectric transducer material, such as PZT-5Havailable from Vernitron, Inc. of Bedford, Ohio. The size of the element18 is a function of the overall size of the transducer 10, however, anelement having a diameter of 0.080 inch and a thickness of 0.003 inchhas been tested experimentally with excellent results. The diameter ofthe element 18 is slightly less than the diameter of the blind bore 36provided in the wear member 12. The element 18 is responsive to a shortvoltage pulse, such as a 200 volt DC pulse of 10 nanosecond duration,and converts the voltage pulse into a pressure pulse which is applied tothe surface of the material whose thickness is to be measured and/ormonitored. Similarly, the piezoelectric element 18 converts the "echo"return pressure pulse from the opposite surface of the material whosethickness is being monitored into a voltage pulse for measurementpurposes. The substantially uniform compressive force applied to thepiezoelectric element 18 by the spacer 16 ensures that the element 18 isfirmly "seated" within the blind bore 36 for the proper transmission ofthe voltage pulse into the element 18 and the reception of the reflected"echo" pulse by the element.

In order to assemble the transducer 10, the piezoelectric element 18 isreceived within the blind bore 36 and positioned so that one side 46thereof contacts the flat surface 42 at the bottom of the blind bore 36.Inasmuch as the diameter of the element 18 is only slightly less thanthe diameter of the blind bore 36, the center of the element 18 and thecenter of the flat surface 42 at the bottom of the blind bore 36 willsubstantially coincide, however, such coincidence is not necessary forthe proper operation of the transducer 10. The other side 48 of thepiezoelectric element 18 may be soldered to an electrical conductor 50.The electrical conductor 50 is received through the aperture 30 providedin the spacer 16, and the spacer 16 is received in the blind bore 36 sothat its base 32 contacts the side 48 of the piezoelectric element 18which is mechanically and electrically connected to the electricalconductor 50. The threads 20 on the outer sleeve 14 are coated with anadhesive, such as Loctite, and the sleeve 14 is threadedly advanced intothe wear member 12 until the conical surface 24 provided on its end 22engages the outer surface 28 of the spacer 16. Further advancement ofthe outer sleeve 14 into the wear member 12 causes the elasticdeformation of the spacer 16 and the indentation in the end 22 of theouter sleeve 14, and the application of a substantially uniformcompressive force by the base 32 of the spacer 16 to the side 48 of thepiezoelectric element 18. If complementary curved configurations, suchas semispherical or parabolic, are used for the spacer 16 and theindentation in the end 22 of the outer sleeve 14, the spacer 16 willself-align itself within the indentation in the end 22 of the outersleeve 14 so that its base 32 will apply a substantially uniformcompressive force to the side 48 of the piezoelectric element 18.Regardless of the shape of the spacer 16 and the indentation in the end22 of the outer sleeve 14, the outer sleeve 14 is threadedly advancedinto the wear member 12 by manually rotating the outer sleeve 14 until asnug fit exists between the indentation provided in its end 22 and theouter surface 28 of the spacer 16, and between the base 32 of the spacer16 and the side 48 of the piezoelectric element 18. In order to ensurethat such a snug fit exists, the foregoing advancement of the outersleeve 14 into the wear member 12 is monitored by a pulser-receiverdevice and an oscilloscope (all not shown). With this apparatus a seriesof short voltage pulses is applied by the pulser to the transducer 10while the outer sleeve 14 is being threadedly advanced into the wearmember 12 so that the sleeve 14 can be rotationally adjusted until theoptimum return "echo" pulse, shown on the oscilloscope, is received bythe receiver. In this manner, a snug fit between the foregoingcomponents is assured and the transducer 10 and the wear member 12 are"tuned" to provide the optimum return "echo" pulse.

Since the piezoelectric element 18 is somewhat formable under acompressive force, the application of a substantially uniformcompressive force thereto results in a firm, optimum electro-acousticalcontact between the side 46 of the element 18 and the flat surface 42 atthe bottom of the blind bore 36. By providing such a firm, optimumelectro-acoustical contact with the flat surface 42 of the blind bore36, any signals emanating from the piezoelectric element 18 will beproperly directed toward the inner surface 40 of the wear member 12 tobe measured and/or monitored, and the wear member 12 will provide theproper electrical ground for the system. Thus, the surfaces 24, 28compensate for deviations in manufacturing tolerances in the componentsinvolved, and the possibility that the blind bore 36 may not bepositioned exactly normal to the inner surface 40 of the wear member 12.Both of these conditions could result in the piezoelectric element 18not firmly contacting the flat surface 42 of the blind bore 36 which, inturn, could result in inaccurate measurements and/or systemmalfunctions. After the transducer 10 has been assembled and installedin the wear member 12, the area 52 enclosed by the inner circumferentialwall 26 of the outer sleeve 14 and containing the electrical conductor50 may be filled with a dense insulating and dampening material such asepoxy, e.g., Duro epoxy, loaded with tungsten for applicationtemperatures less than 400° F. or a loaded ceramic adhesive fortemperatures in excess of 400° F. This electric insulation material andthe spacer 16 preferably match the acoustical impedance of thepiezoelectric element 18 and help suppress spurious echoes, which arelater in time and thus much weaker than the primary ultrasonic pressurepulse, from interferring with the primary pulse. After the installationof the transducer 10 in the wear member 12 has been completed, an epoxymay be placed on the outer surface of the sleeve 14 adjacent the topsurface of the wear member 12 to prevent any contaminants from enteringthe transducer.

The wear member 12 may have a configuration that is either flat, such asa brake disc, clutch plate, face type seal or thrust type bearing, orcircular, such as a sleeve bearing or ring type seal. In any case, aplurality of transducers can be utilized to measure and/or monitor wearat various locations on the wear member 12. If a sleeve bearing isutilized, the plurality of transducers 10 can be placed within the outerbearing wall and around the periphery of the bearing, as shown in FIG.2. In this manner, bearing wear can be measured and/or monitored aroundthe periphery thereof. Thus, by placing the transducer 10 within one ormore blind bores 36 within the bearing, wear can be measured and/ormonitored in-situ, eliminating costly periodic machine downtime toinspect the condition of the bearing. Machine downtime would only occurwhen a transducer indicates that sufficient wear has occurred to justifythe replacement of the bearing.

Alternatively, rather than placing a plurality of transducers 10 withinthe blind bores provided in the outer bearing wall, a mountingattachment 54, such as a ring as shown in FIG. 3, could be used toretain the transducers 10 in a radially spaced apart relationship. Insuch an arrangement, the mounting attachment 54 would be slipped overthe sleeve bearing 56 and the piezoelectric elements 18 would firmlycontact the outer surface of the bearing wall. Thus, no blind boreswould be required in the bearing wall. In this arrangement, since theradius of the curvature of the bearing 56 is substantially greater thanthe diameter of each piezoelectric element 18 and inasmuch as asubstantial compressive force is being applied to each element 18 by itsassociated spacer 16, it has been found that sufficient surface contactexists between each element 18 and the outer surface of the bearing 56to produce very accurate distortionless measurements of wall thickness.Thus, by using this apparatus, the total bearing wall thickness can bemeasured and/or monitored at various locations on the bearing.

In addition to being able to measure wear in-situ, the construction ofthe transducer 10 provides another advantage in that no buffer elementis required between the piezoelectric element 18 and the wall whosethickness is being measured and/or monitored, i.e., the distance betweenthe flat surface 42 of the blind bore 36 and the inner surface 40 of thewear member 12. Typically, in prior art devices such a buffer element isrequired for mechanical support, impedance matching and sealing of thetransducer, however, its use greatly attenuates and degrades the primarypulses produced by the transducer and the reflected "echo" pulsesreceived by the transducer. Inasmuch as the transducer 10 requires nobuffer element, such signal attenuation and degradation does not occur.In addition, because of the absence of a buffer element, a firmelectrical and acoustical contact can be made by the piezoelectricelement 18 directly to the wall thickness being measured and/ormonitored, and the resulting measurements have a much higher degree ofaccuracy than those resulting from prior art devices. For example,measurements with a repeatability in the sub-micron range utilizingstate-of-the-art electronics have been achieved. And lastly, due to theinherent simplicity of the structure of the transducer, it issubstantially less costly to produce than the prior art devices.

In an alternate embodiment of the invention, as shown in FIG. 4, theblind bore 36 in the wear member 12 is replaced with a through bore 60connecting the outer and inner surfaces 38, 40 of the member 12. Thethrough bore 60 may have threads 62 formed therein. A transducer 64comprising an outer sleeve 14, a spacer 16, and a piezoelectric element18 is received within a blind bore 66 in a wear reference member 68which may have threads 70 formed on the outer surface thereof. The wearreference member 68 is received within the through bore 60 so that itsend 72 is substantially flush with the inner surface 40 of the wearmember 12. The inner surface 40 of the wear member 12 is then machinedto ensure that the end 72 of the wear reference member 68 is flush withthe inner surface 40. It should be noted that the material utilized forthe wear reference member 68 may be the same as or may be different fromthe material comprising the wear member 12 inasmuch as only thethickness of the end of the reference member 68 is being monitoredand/or measured. The operation of this embodiment is similar to theprevious embodiment utilizing a blind bore, however, it is easier andless costly to produce.

With any of the foregoing embodiments, it might be desired to compensatefor the temperature and pressure of the environment, the density of thematerial utilized for the transducer, and the strains existing on thetransducer. Such compensation can be accomplished by using a timereference transducer 80, as shown in FIG. 5. The structure of thistransducer 80 is similar to transducer 10, in that it is comprised of anouter sleeve 14, a spacer 16, and a piezoelectric element 18, however,the foregoing components are received in a blind bore 82 provided in areference member 84, which is similar to wear reference member 68. Thematerial utilized for the reference member 84 is the same as or similarto the material for the wear member 12 if a blind bore 36 is utilized inthe member 12, or the same as or similar to the material for the wearreference member 68 if a through bore 60 is provided in the wear member12. The assembly of the transducer 80 and the reference member 84 isplaced within the same temperature, pressure or material environment asthe other transducers 10, though not necessarily contacting the wearmember 12. By monitoring the measurements of the reference distance,produced by the transducer 80, the measurements produced by thetransducers 10 can be adjusted to compensate for possible measurementvariations caused by operating environment changes.

Certain modifications and improvements will occur to those skilled inthe art upon reading the foregoing. It should be understood that allsuch modifications and improvements have been deleted herein for thesake of conciseness and readability, but are properly within the scopeof the following claims.

We claim:
 1. An ultrasonic transducer device for measuring the thicknessof a member comprising a piezoelectric element and means for biasingsaid piezoelectric element against a surface of the member whosethickness is to be measured, said biasing means comprising a sleevehaving a recess provided in one end thereof and spacer means receivedwithin said recess in said sleeve so that a portion of the surfacedefining said recess contacts a portion of the surface of said spacermeans, said recess and said spacer means having complementary non-linearconfigurations and said contacting surface portions on said recess andsaid spacer means both having substantially continuous configurationspermitting the alignment of said spacer means within said recess, saidspacer means also having a substantially flat surface thereon whichcontacts said piezoelectric element and applies a substantially uniformforce across the entire surface of said piezoelectric element.
 2. Thetransducer device as defined in claim 1 wherein said piezoelectricelement has a pair of faces, one of said pair of faces being on contactwith a surface of the member whose thickness is to be measured and theother of said pair of faces being compressed by said spacer means. 3.The transducer device as defined in claim 2 further including anelectrical conductor operatively connected to said piezoelectricelement, said electrical conductor being received through said sleeveand said spacer means for connection to said piezoelectric element. 4.The transducer device as defined in claim 3 wherein said electricalconductor is operatively connected to said other of said pair of facesof said piezoelectric element.
 5. The transducer device as defined inclaim 3 further including insulating means received within said sleeve,said insulating means being positioned so as to be in a surroundingrelationship with said electrical conductor.
 6. The transducer device asdefined in claim 5 wherein said insulating means comprises a materialwhich substantially matches the acoustical impedance of the transducerdevice.
 7. The transducer device as defined in claim 1 wherein saidsurface defining said recess in said sleeve has a conical configurationwhich contacts the surface of said spacer means.
 8. The transducerdevice as defined in claim 1 wherein the surface of said spacer meanshas a conical configuration which contacts said surface defining saidrecess in said sleeve.
 9. The transducer as defined in claim 1 whereinsaid complementary non-linear configurations are conical in shape. 10.The transducer as defined in claim 9 wherein said conical complementaryconfigurations for said recess and said spacer means permit said spacermeans to be aligned within said recess through elastic deformation ofsaid spacer means.
 11. The transducer as defined in claim 1 wherein saidcomplementary non-linear configurations are curved in shape.
 12. Thetransducer device as defined in claim 11 wherein said curvedcomplementary configurations for said recess and said spacer meanspermit said portion of said surface of said spacer means to slidinglyengage said portion of said surface defining said recess in said sleeveallowing self-alignment of said spacer means within said recess.
 13. Thetransducer device as defined in claim 1 wherein said sleeve has threadsformed on the outer surface thereof adjacent said one end thereof, saidthreads permitting the attachment of said transducer device to a memberwhose thickness is to be measured.
 14. A device for measuring thethickness of a member in-situ comprising, in combination, apiezoelectric element, a member whose thickness is to be measured, andmeans for biasing said piezoelectric element against a surface of saidmember whose thickness is to be measured, said biasing means comprisinga sleeve having a recess provided in one end thereof and spacer meansreceived with said recess in said sleeve so that a portion of thesurface defining said recess contacts a portion of the surface of saidspacer means, said recess and said spacer means having complementarynon-linear configurations and said contacting surface portions on saidrecess and said spacer means both having substantially continuousconfigurations permitting the alignment of said spacer means within saidrecess, said spacer means also having a substantially flat surfacethereon which contacts said piezoelectric element and applies asubstantially uniform force across the entire surface of saidpiezoelectric element.
 15. The combination as defined in claim 14wherein said piezoelectric element has a pair of faces, one of said pairof faces being in contact with said member whose thickness is to bemeasured and the other of said pair of faces being compressed by saidspacer means.
 16. The combination as defined in claim 15 wherein saidmember has a blind bore provided therein, said piezoelectric elementbeing received within said blind bore allowing said one of said pair offaces of said piezoelectric element to contact the bottom surface ofsaid blind bore.
 17. The combination as defined in claim 15 furtherincluding an electrical conductor operatively connected to saidpiezoelectric element, said electrical conductor being received throughsaid sleeve and said spacer means for connection to said piezoelectricelement.
 18. The combination as defined in claim 17 wherein saidelectrical conductor is operatively connected to said other of said pairof faces of said piezoelectric element.
 19. The combination as definedin claim 17 further including insulating means received within saidsleeve, said insulating means being positioned so as to be in asurrounding relationship with said electrical conductor.
 20. Thecombination as defined in claim 19 wherein said insulating meanscomprises a material which substantially matches the acousticalimpedance of the transducer device.
 21. The combination as defined inclaim 14 wherein said surface defining said recess in said sleeve has aconical configuration which contacts the surface of said spacer means.22. The combination as defined in claim 14 wherein the surface of saidspacer means has a conical configuration which contacts said surfacedefining said recess in said sleeve.
 23. The combination as defined inclaim 14 wherein said complementary non-linear configurations areconical in shape.
 24. The combination as defined in claim 23 whereinsaid conical complementary configurations for said recess and saidspacer means permit said spacer means to be aligned within said recessthrough elastic deformation of said spacer means.
 25. The combination asdefined in claim 14 wherein said complementary non-linear configurationsare curved in shape.
 26. The combination as defined in claim 25 whereinsaid curved complementary configurations for said recess and said spacermeans permit said portion of said surface of said spacer means toslidingly engage said portion of said surface defining said recess insaid sleeve allowing self-alignment of said spacer means within saidrecess.
 27. The combination as defined in claim 14 wherein said memberwhose thickness is to be measured provides conductive properties and theelectrical ground for the combination.
 28. A device for measuring thethickness of a member in-situ at various locations thereon comprising,in combination, a plurality of piezoelectric elements, a member whosethickness is to be measured at various locations thereon, and means forbiasing one of said plurality of piezoelectric elements against saidmember so as to contact said member at each of said measurementlocations, said baising means comprising a sleeve having a recessprovided in one end thereof and spacer means received within said recessin said sleeve so that a portion of the surface defining said recesscontacts a portion of the surface of said spacer means, said recess andsaid spacer means having complementary non-linear configurations andsaid contacting surface portions on said recess and said spacer meansboth having substantialy continuous configurations permitting thealignment of said spacer means within said recess, said spacer meansalso having a substantially flat surface thereon which contacts saidpiezoelectric element and applies a substantially uniform force acrossthe entire surface of said piezoelectric element.
 29. The combination asdefined in claim 28 wherein said various measurement locations on saidmember are in a pre-determined arrangement.
 30. The combination asdefined in claim 28 wherein said member provides conductive propertiesand the electrical ground for the combination.
 31. A method formeasuring the thickness of a member in-situ through the use of anultrasonic transducer device comprising a piezoelectric element andmeans for biasing said piezoelectric element against a surface of themember whose thickness is being measured, said biasing means comprisinga sleeve having a recess provided in one end thereof and spacer meansreceived within said recess in said sleeve so that a portion of thesurface defining said recess contacts a portion of the surface of saidspacer means, said recess and said spacer means having complementarynon-linear configurations and said contacting surface portions on saidrecess and said spacer means both having substantially continuousconfigurations permitting the alignment of said spacer means within saidrecess, said spacer means also having a substantially flat surfacethereon which contacts said piezoelectric element and applies asubstantially uniform force across the entire surface of saidpiezoelectric element, said method comprising the steps of:locating saidultrasonic transducer device within the member whose thickness is beingmeasured; applying a pulse to said ultrasonic transducer device causingsaid piezoelectric element to transmit an interrogating signal into themember whose thickness is being measured; receiving a return signal fromthe member whose thickness is being measured in response to saidinterrogating signal; and processing said interrogating signal and saidreturn signal to determine the thickness of the member.
 32. A method fordetermining the amount of wear which has occurred to a member in-situ bymeasuring the change in thickness of the member over a period of timethrough the use of an ultrasonic transducer device comprising apiezoelectric element and means for biasing said piezoelectric elementagainst a surface of the member whose change in thickness is beingmeasured, said biasing means comprising a sleeve having a recessprovided in one end thereof and spacer means received within said recessin said sleeve so that a portion of the surface defining said recesscontacts a portion of the surface of said spacer means, said recess andsaid spacer means having complementary non-linear configurations andsaid contacting surface portions on said recess and said spacer meansboth having substantially continuous configurations permitting thealignment of said spacer means within said recess, said spacer meansalso having a substantially flat surface thereon which contacts saidpiezoelectric element and applies a substantially uniform force acrossthe entire surface of said piezoelectric element, said method comprisingthe steps of:locating said ultrasonic transducer device within themember whose change in thickness is being measured; applying a pulse tosaid ultrasonic transducer device causing said piezoelectric element totransmit a first interrogating signal into the member; receiving a firstreturn signal from the member in response to said first interrogatingsignal; processing said first interrogating signal and said first returnsignal to determine a first thickness of the member; applying a pulse tosaid ultrasonic transducer device causing said piezoelectric element totransmit a second interrogating signal at a later time into the member;processing said second interrogating signal and said second returnsignal to determine a second thickness of the member; and processingsaid first thickness determination and said second thicknessdetermination to determine the change in thickness which has occurred tothe member.